Don’t get in too deep with potato establishment
Potato growers are frequently cultivating too deep when preparing beds and need to revise their machinery management to avoid compaction and yield penalties, warns an expert.
According to research, most damage is done by the bed-tilling and destoning operations prior to planting, as they work across the whole width of the bed.
With that in mind, Cambridge University Farm (CUF) cultivations expert Mark Stalham asks the question, what is the optimum bed depth?
“Most varieties only need 15cm of settled soil over the top of the seed to reduce greening and possibly as little as 10-12cm for salad and seed crops,” says Dr Stalham.
| Potato planter set-up tips |
|---|
Standen Pearson chief engineer Phil Smith offers a few tips for getting cup potato planters running like a dream.
|
“With this taken into consideration, most growers are working far too deep in some situations, with few tubers forming at the depth that soil has been worked to,” he explains.
Dr Stalham points out that most growers are working their destoners to produce beds at 34-36cm, which is about 8-10cm deeper than is required to achieve a bed able to support the crop without negative yield and quality effects.
Bed-forming
Many are starting off on the wrong foot by bed-forming too deep, but this operation causes little damage in itself, only smearing and compacting about 30% of the bed.
Furrows in-between beds need to be deep enough to bury any stones/clods that the destoner removes, so where the soil is likely to be less stony or cloddy, the operator can afford to reduce depth.
“Growers seem to be managing everything for the worse-case scenario, but in many cases you can cultivate shallower and less vigorously on each pass and have no detrimental effect on the crop,” Dr Stalham explains.
It can also be argued that on heavy soils, the deeper you work with a destoner, the shallower the bed will become, as the machine will actually produce more clods.
“It is about finding the optimum depth to minimise damage to structure where the soil remains plastic, but creating enough tilth to give the optimum conditions for harvesting without damage,” says Dr Stalham.
He also urges caution when letting formed beds dry out before they are declodded, as it can also result in too much being taken from the ridge.
Operator management
When considering working depth on destoners, Dr Stalham advises growers to manage their operators with more flexibility, adjusting the machine to suit soil type and ground conditions.
Cost savings compliment the benefits to soil structure, particularly when working on heavier soils.
On lighter land, it’s unlikely that destoners will cause compaction damage by working at depth, however working unnecessarily at increased depths will slow work rate and increase fuel consumption.
| CUFs establishment essentials |
|---|
|
“Bringing working depth up 5cm can result in 10% less fuel consumption or a saving of 5% of your cultivation fuel bill,” Dr Stalham says.
Although that sounds like a very small gain, Dr Stalham is quick to point out that yield and quality isn’t affected and any saving is worthwhile.
“On heavier land it is much more significant, though. You are damaging soil structure, compromising yield and quality and using far more fuel,” he adds.
Typically, that same 5cm adjustment to destoner depth will gain you about 14-18% on fuel, with the proportion of total fuel costs closer to 10%.”
Reduction in depreciation, breakdown time and labour from working the machines harder and slower would result in further savings to cost of production.
“We must convince growers of the potential savings in cost and the value of preventing yield reductions and improving tuber quality,” he adds.
Sad soils
Slumped soils could be an issue this season, with anaerobic soils having a much greater water-holding capacity higher up the soil profile.
Dr Stalham advises that on heavier sandy loams, destoners should be working shallower to avoid further compaction issues later in the season. “People need to start paying attention to what their destoner is doing. Decreasing pore size too far may even cause slumping of the bed in the season, so ensure machines aren’t working too vigorously,” he concludes.
| Seed grading and cup size crucial |
|---|
Although bed formation and preparation are the vital building blocks of potato crop establishment, when it comes to getting seed in the ground there are still some important aspects to consider. Seed should be graded as tightly as possible, says Dr Stalham, to ensure good performance by cup planters. Cup size can be manipulated by cup inserts, which usually come in two sizes. Standen Pearson cup planters offer the factory-fitted cup (45mm+) that can be adjusted with a small insert (25-35mm) and a medium insert (35-45mm). Incorrect cup sizes and poorly-graded seed can result in doubles, where the cups pick up two small seed potatoes. Misses can also occur where large seed tubers fall off cups. Both affect saleable yield. “Changing cups can be very time-consuming and I’m not sure many growers would be changing them as regularly as needed when swapping seed size,” says Dr Stalham. Accuracy of seed placement can also be affected by forward speed, which is one of the limitations of the cup planter. The physical limit for most cup planters is about 4-5km/hour. “After this belt planters take over, but they are less accurate.” Firm flanks Once at least 15cm of soil covers the seed tuber, it is the overall shape of the bed and not planting depth that will have the greatest effect on yield, according to Dr Stalham, and he urges growers to be smarter as to where they put the soil. One way to ensure there are fewer green tubers is to have more soil on the flanks of the bed, to reduce the negative effect of wash-off or erosion from tractor tyres in the row. It is possible to do this by moving the seed closer to the centre of the bed, further from the shoulder, says Dr Stalham, therefore reducing the risk of exposing tubers. Initial research has shown that hood pressure at the back of the planter to consolidate the bed has no positive effect on emergence of the crop, but it can have a negative effect. This is particularly prevalent on moist, heavier soils, where smearing and compaction can also be an issue and crop emergence slower. “Growers should keep it as simple as possible when planting – the more you do, the more draught and compaction you create, increasing fuel use, machinery wear and slowing establishment,” explains Dr Stalham.”
|
